The present invention relates to a flame-retardant resin composition or, more particularly, to a method for imparting flame-retardancy to a synthetic resin or, in particular, thermoplastic resin to give a resin composition outstandingly safe from the troubles due to dripping of the molten composition under burning.
It is a heretofore established technology that thermoplastic resins can be imparted with flame retardancy when compounded with various kinds of flame retardant agents including halogen-containing compounds, phosphorus-containing compounds, antimony trioxide and the like either singly or as a combination of two kinds or more according to need. It is known, in particular, that a synergistically improved flame retardant effect can be obtained by the combined use of a halogen-containing compound and a phosphorus-containing compound as the flame retardant agent. The use of a halogen-containing compound or antimony trioxide as the flame retardant agent, however, has a serious problem that highly toxic gases such as hydrogen halides and antimony halides are produced when a shaped article of the resin compounded with these flame retardant agents is burnt. A solution of this problem is eagerly desired along with a high flame retardant effect in the fields of household electric appliances manufactured by using various kinds of synthetic resins compounded with a flame retardant agent free from generation of any toxic gases by burning.
In this regard, extensive investigations are now under way to discover a non-halogen compound capable of exhibiting an excellent flame retardant effect when compounded with a synthetic resin. For example, application of silicones or, namely, organopolysiloxane compounds and organosilane compounds is highlighted because silicones in general are physiologically inert and safe from generation of toxic gases under burning. Japanese Patent Kokai No. 1-108235 discloses a method according to which a metal hydroxide powder as a class of flame retardant agents is surface-treated with a silane coupling agent so as to be imparted with improved water resistance and acid resistance. Japanese Patent Publication No. 3-48947 proposes the use of a crosslinkable silicone fluid and a so-called MQ resin in combination as a non-halogen flame retardant agent in synthetic resins. Japanese Patent Kokai No. 64-14277 proposes a further combined use of a phosphorus-containing compound to the above. None of these prior art flame retardant agents, however, is quite satisfactory in respect of the preventing effect against dripping of the melt of the resin under burning. In particular, polystyrenes and styrene-based resins, which are notorious in respect of the difficulty of being imparted with a sufficiently high effect of flame retardancy not to cause dripping of the melt by compounding with conventional flame retardant agents.